A network consists of a group of switches (nodes) interconnected by a variety of interface types, for example optical interfaces. The SSCOP is a signaling protocol that guarantees reliable communication between nodes. The call control of a transmitting node sends packeted information to the SSCOP. The SSCOP encapsulates the packets and transmits the packets over a link to the SSCOP of another node where it is decoded and forwarded to the call control of the receiving node.
In some packet-based data transfer technologies, for example, ATM, the establishment of a connection between the call originator and call receiver requires the internodal exchange of resource capability information. However, ATM switches support several kinds of interface protocols, for example, user-network interfaces (UNIs) that connect end-systems, such as routers, to an ATM switch, private network—network interfaces (PNNIs) that are used for connections between networks, and ATM inter-network interfaces (AINIs). Each of these interfaces runs on its own protocol.
The resource capability information exchanged between nodes may include bandwidth allocation, virtual path identifier (VPI)/virtual channel identifier (VCI) ranges, type of interface and protocol that the node supports, and other information. Typically, this resource capability information is exchanged through a management plane protocol known as the interim local management interface (ILMI) protocol.
The ILMI protocol communicates between two nodes to determine the resource parameters of each and automatically configures the connection. For example, the VPIs and VCIs are of varying length and may have different lengths at different nodes. The number of bits allocated to represent the VPI and the VCI determine the range of possible VPIs and VCIs for that node. The ILMI protocol may determine that the VPI/VCI range of a given switch is 0–255/0–15 and the VPI/VCI range of another switch is 0–15/0–3. Restrictions within the common range are then made on the VPI/VCI to be used between the switches. Through ILMI polling of the switches, a common VPI/VCI range can be found and the internodal connection configured automatically.
ILMI falls short when the switches involved use partition-based resource allocation (i.e., link partitioning). Links may be logically partitioned allowing a single physical link to be viewed logically as two or more links. This logical partitioning allows different protocols (e.g., IP) to be transmitted over the same link. This is accomplished by dividing the resource range. For example, a switch that allocates 16 bits for its VPI may allocate 0 through 255 for PNNI data and 256–4095 for MPLS data and may allocate other ranges for other protocols. The ILMI protocol operates based on certain assumptions that are incompatible with a partitioned link scheme. One assumption that ILMI protocol operates on is that, on a link basis, the minimum VPI is one. This holds true for a non-partitioned link with only one protocol running, but not for partitioned links. Since a partitioned link may have, for example, PNNI protocol allocated from 0–255 and MPLS protocol allocated from 256–4095, the minimum VPI could be 256. If the resource configuration cannot be negotiated then the connections cannot be established and resources are wasted.
Further drawbacks of the ILMI protocol are that it is not applicable to all ATM protocols, for example, AINI. Therefore, such protocols may require manual resource configuration. ILMI is not designed to run on virtual trunks, i.e., ILMI is link-specific. And the full capabilities of ILMI are not required in all contexts and therefore running the ILMI protocol may unnecessarily tax system performance.